All radiograms have a preamble, consisting of the following parts:
HX - Handling Instructions
Place of Origin
Month / Day
The message number is assigned by the station originating the message. This number is permanently assigned to the message through to the point of delivery. Understand that with a Service Message, the letters SVC can be placed in front o fthe message number. However, this appears to not be used frequenlty these days.
Numbers are assigned by the operator of the station originating the message at their discretion.